Maint: Fix order dependent test failure

Previously, executing the following would fail due to order dependent
test failures:

  rspec spec/unit/util/virtual_spec.rb spec/unit/util/macaddress_spec.rb
  rspec spec/unit/util/virtual_spec.rb spec/unit/util/uptime_spec.rb

This occurs because rspec filters were being used on describe blocks,
but those values are not cleared up between examples.

This commit instead filters the tests based on
Facter::Util::Config.is_windows?

It also removes duplicate expectations on kernel value